System and method for providing mobility management and out-of-coverage indication in a conventional land mobile radio system

CROSS-REFERENCE TO RELATED APPLICATIONS

p-0002Pursuant to 35 U.S.C. §119(e), this application claims priority from, and hereby incorporates by reference for all purposes, U.S. Provisional Patent Application Ser. No. 61/398,919, entitled “System and Method for Providing Mobility Management and Out-of-Coverage Indication in a Conventional Land Mobile Radio System,” filed Jun. 30, 2010, and naming Arindam Roy, Linda Trine, and Marshall Jobe as inventors.

TECHNICAL FIELD

p-0003The present invention relates generally to Land Mobile Radio (LMR) systems and, more specifically, to a system and method that allows users operating in a conventional system, such as, for example, a Project 25 conventional system, to achieve mobility management and out-of-coverage indication.

BACKGROUND

p-0004Land Mobile Radio (LMR) systems are deployed by organizations requiring instant communication between geographically dispersed and mobile personnel. Typical users of LMR systems include police departments, fire departments, medical personnel, security personnel, EMS, and the military.

p-0005Current LMR systems can be configured to provide for radio communications between one or more sites and subscriber radio units in the field. A subscriber radio unit (hereinafter “radio”) may be a mobile unit or a portable unit. LMR systems can be as simple as two radio units communicating between themselves and a site over preset channels, or they can be complex systems that include hundreds of radio units and multiple sites.

p-0006LMR systems can be broadly divided into two classes: (1) trunking LMR systems; and (2) conventional LMR systems. A trunking system generally includes one or more trunking sites and dispatch control centers. <figref idrefs="DRAWINGS">FIG. 1</figref> illustrates a typical trunking LMR system <b>100</b> including a trunking site <b>104</b> and a dispatcher <b>108</b>. The trunking site <b>104</b> includes a control channel <b>112</b> and one or more traffic channels (e.g., <b>116</b>, <b>118</b>). Typically a group of radio users (e.g., <b>124</b>, <b>128</b>) create a user group to communicate with each other and the dispatcher <b>108</b>. In a trunking system <b>100</b> there can be multiple radio users and multiple user groups.

p-0007Trunking systems streamline usage of Radio Frequency (RF) resources (e.g., traffic channels) through the use of mobility management. Mobility management allows the system to send periodic messages to the radios through a dedicated radio frequency base station, also known as a control channel, while the radios communicate back with the system. Said periodic messages may indicate coverage availability, signal strength, and other data to the radio, while communication from the radio may indicate to the system the radio's location and interested user group. If the radio stops receiving the messages from the control channel <b>112</b>, the radio notifies the user, typically through visual and audible indicators, that the radio is outside of the coverage zone of the trunking system.

p-0008Mobility management allows dynamic routing of “Push-to-Talk” user group calls based on user availability in different geographic locations. Therefore, trunking systems implement mobility management to allow a radio unit to move from one geographic region to another while the system keeps track of the unit's location and user group affiliation within the unit's current geographic region. When a radio user wants to contact other radio users or a dispatcher in the same user group, the radio user sends a request to a trunking site controller <b>132</b> through the control channel <b>112</b>. The trunking site controller <b>132</b> contacts the other trunking sites interested in the same user group. The trunking site controller in each interested site allocates an available traffic channel. Once a channel is available, the radio users in the user group are notified through the control channel, and their radios are placed in communication with the appropriate traffic channel to communicate with each other. Since a traffic channel is allocated dynamically on a per call basis, a trunking system provides efficient utilization of available bandwidth and RF resources.

p-0009Although trunking systems provide efficient usage of RF resources, it is achieved at significant costs. Specifically, the control channel required to provide communication of user location from the radios to the system is expensive. When cost is of concern, a conventional LMR system may be a preferred solution since the conventional system lacks the expensive control channel.

p-0010A conventional system allows the radio users to directly access a traffic channel, if available, and originate voice communication. <figref idrefs="DRAWINGS">FIG. 2</figref> illustrates a conventional LMR system <b>200</b>. Like the trunking system <b>100</b>, the conventional LMR system <b>200</b> may include one or more conventional sites, although only one conventional site <b>204</b> and dispatcher <b>208</b> is shown in <figref idrefs="DRAWINGS">FIG. 2</figref>. However, unlike the trunking site <b>104</b>, the conventional site <b>204</b> does not include a control channel. The conventional site <b>204</b> includes one or more traffic channels (e.g., <b>216</b>, <b>220</b> and <b>224</b>) each traffic channel being typically assigned to one or more user groups for use by radios, such as radio <b>228</b> and radio <b>232</b>. The members of a user group may communicate with each other on the same traffic channel, thus allowing the users and the dispatcher to instantly communicate with each other without waiting for the system to allocate a traffic channel.

p-0011Although a conventional system may be more economical, one of its disadvantages is that the absence of a control channel precludes the system from sending periodic coverage indication messages to the radios, and the radios are unable to inform the system of its location or interested user group—features typically associated with mobility management as discussed above. Therefore, the system is unable to intelligently route originating traffic to select destination sites based on user availability, and the radio is unable to indicate to the user that the radio is outside of the coverage zone of the conventional system. As a result, a conventional system implements preconfigured routing to route the call from the originating radio to a fixed set of geographic locations, regardless of user availability in those sites. Accordingly, RF resources are typically wasted or inefficiently allocated when a user is not available in a site. While a conventional system may provide an initial lower cost LMR system solution, the lack of mobility-based routing and out-of-coverage indication limits the usage and capabilities of the system.

SUMMARY

p-0012The present disclosure provides a system and a method for providing mobility management and out-of-coverage indication in a conventional system, thus maintaining the lower initial costs associated with a conventional system while concurrently enhancing the system to provide operation similar to that of a trunking system.

p-0013The foregoing and other features and advantages of the present disclosure will become further apparent from the following detailed description of the embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the disclosure, rather than limiting the scope of the invention as defined by the appended claims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

p-0014Embodiments are illustrated by way of example in the accompanying figures, in which like reference numbers indicate similar parts, and in which:

p-0015<figref idrefs="DRAWINGS">FIG. 1</figref> is an illustration of an exemplary trunking LMR system;

p-0016<figref idrefs="DRAWINGS">FIG. 2</figref> is an illustration of an exemplary conventional LMR system;

p-0017<figref idrefs="DRAWINGS">FIG. 3</figref> is a general illustration of an exemplary embodiment of the disclosed system;

p-0018<figref idrefs="DRAWINGS">FIG. 4</figref> is a more detailed illustration of a site of the system shown in <figref idrefs="DRAWINGS">FIG. 3</figref>;

p-0019<figref idrefs="DRAWINGS">FIG. 5</figref> illustrates the steps and components involved in an exemplary initial check of a mobility update event occurring within a local site;

p-0020<figref idrefs="DRAWINGS">FIG. 6</figref> is an updated version of <figref idrefs="DRAWINGS">FIG. 5</figref> illustrating the steps and components involved in an exemplary mobility update event after it has been determined that the mobility update is to be pushed to the rest of the system; and

p-0021<figref idrefs="DRAWINGS">FIG. 7</figref> illustrates an example embodiment of a method for providing mobility management and out-of-coverage indication in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

p-0022The present disclosure provides a system and a method for providing mobility management and out-of-coverage indication in a conventional LMR system. The disclosed system and method allows operability similar to that of a trunking system by providing mobility management and out-of-coverage indication while providing, in certain implementations, low-cost benefits through operation of a conventional system.

p-0023<figref idrefs="DRAWINGS">FIG. 3</figref> provides an overview of an exemplary embodiment of the system <b>300</b> disclosed herein. The exemplary system <b>300</b> shown in <figref idrefs="DRAWINGS">FIG. 3</figref> includes a home location <b>310</b> and conventional LMR sites <b>320</b>A, <b>320</b>B, and <b>320</b>C (also referred to herein as “sites”). The system <b>300</b> may comprise a data router <b>330</b>, and dispatch consoles <b>340</b>A, <b>340</b>B, and <b>340</b>C. When reference is made herein to a generic site or to all the sites, reference number <b>320</b> may be used; otherwise, when reference is made to a specific site, the corresponding site reference number (e.g. <b>320</b>A, <b>320</b>B, or <b>320</b>C) may be used. Additionally, the term “local site” may be used herein to reference a single site of interest without defining the site of interest as a particular site, and the term “remote site” may be used to refer to a site other than the local site. When reference is made to a generic dispatch console or to all the dispatch consoles, reference number <b>340</b> may be used; otherwise, when reference is made to a specific dispatch console, the corresponding dispatch console reference number (e.g., <b>340</b>A, <b>340</b>B, or <b>340</b>C) may be used. Although <figref idrefs="DRAWINGS">FIG. 3</figref> only shows three sites <b>320</b> and dispatch consoles <b>340</b>, it should be understood that the system <b>300</b> may accommodate a lesser or greater number of sites <b>320</b> and dispatch consoles <b>340</b>.

p-0024In an embodiment of the present disclosure, the home location <b>310</b> may include a network management system (NMS) <b>312</b>, central database <b>314</b> and home location register (HLR) <b>316</b>. In general, the NMS <b>312</b> supports system-wide configuration of all components in the system <b>300</b>, as well as statistics tracking, alarm tracking, and other system management functionality; the central database <b>314</b> stores data; and the HLR <b>316</b> works together with a visitor location register (VLR) located at or assigned to each site <b>320</b> to track user group data and the location of all radios in the system <b>300</b>. In some embodiments, the central database <b>314</b> may be combined, partitioned or associated with the NMS <b>312</b> and/or HLR <b>316</b>.

p-0025Each site <b>320</b> handles communications with and between radios and the system <b>300</b>. In an embodiment of the present disclosure, each site <b>320</b> may include a radio tower <b>321</b>, a network interface unit (NIU) <b>322</b>, a local database <b>323</b>, a VLR <b>324</b>, and a repeater <b>325</b> such as, for example, the 2600 Series Repeater manufactured by EF Johnson. The repeater <b>325</b>, in this embodiment, receives and transmits digital and/or analog signals between the radios (not shown in <figref idrefs="DRAWINGS">FIG. 3</figref>) and the local site <b>320</b>. The radio tower <b>321</b> provides a communication medium between the repeater <b>325</b> and the radios. Although it is not shown in <figref idrefs="DRAWINGS">FIG. 3</figref>, the NIU <b>322</b> may house site applications (e.g., site controller application, channel controller application, inter-site router application, and 2/4-wire interface application). The NIU <b>322</b> and its internal applications perform radio and user group validation functions as well as coordinate inter-site calls between radios and/or calls between 2 or 4-wire devices such as, for example, tone remotes or analog repeaters. The VLR <b>324</b> and local database <b>323</b> may reside within the NIU <b>322</b>; however, they are shown separately in <figref idrefs="DRAWINGS">FIG. 3</figref> (and the following figures) in order to better illustrate the specific components in the system <b>300</b> involved in mobility management. Additionally, although in <figref idrefs="DRAWINGS">FIG. 3</figref> each site <b>320</b> is shown to have its own NIU <b>322</b>, VLR <b>324</b> and local database <b>323</b>, in other embodiments multiple sites <b>320</b> may share a single NIU <b>322</b>, VLR <b>324</b> and local database <b>323</b>.

p-0026The data router <b>330</b> is operable to communicate with the NIU <b>322</b> located in one or more of the sites <b>320</b> to track the location of a radio, and route data between the proper components of the system <b>300</b>. In some embodiments, the radio location may be considered to be the site to which the radio is communicating, a geographical location, coordinate data such as that provided by a Global Positioning System (GPS), or some combination thereof. The dispatch consoles <b>340</b> are operable to communicate with their respective sites <b>320</b> and other dispatch consoles <b>340</b> to determine whether radios belonging to a specific user group are located at a particular site <b>320</b>, and to direct communication between each of the sites <b>320</b>. Although tracking of a radio may be provided by the data router <b>330</b>, in some embodiments, this functionality may be provided by other components such as, for example, the HLR <b>316</b>.

p-0027Typically, a radio is considered to be within coverage of the system <b>300</b> when it is operable to communicate with one or more of the sites <b>320</b> in the system <b>300</b>. Although a radio may be outside the coverage zone of a particular site <b>320</b>, it may still be considered within coverage of the system <b>300</b> as long as the radio is within coverage of at least one of the other sites <b>320</b> in the system <b>300</b>. A radio within coverage is operable to communicate with the system <b>300</b> and other radios, whereas a radio out-of-coverage is unable to communicate with the system <b>300</b> and other radios. In accordance with an embodiment of the present disclosure, a radio operating within the disclosed system <b>300</b> may provide an audible, visual, vibration, or some other out-of-coverage indication to alert the user that the radio is outside the coverage zone of the system <b>300</b>.

p-0028In accordance with the present disclosure, when a specific component corresponding to a specific site <b>320</b> is referenced, the component may be referenced according to the specific site <b>320</b> in which the component is located by appending the letter associated with the specific site to the component's generic reference number. For example, the generic reference number for a local database is “<b>323</b>.” If reference is made to the local database of site <b>320</b>A, the local database may be referenced as “<b>323</b>A.” Accordingly, if reference is made to the local databases of sites <b>320</b>B and <b>320</b>C specifically, the local databases may be referenced as “<b>323</b>B” and “<b>323</b>C,” respectively. Unless indicated otherwise, when a component is referenced by its generic reference number, it should be understood that the reference may include all, or any one, of the components located within the system <b>300</b>. For example, in accordance with the previous example, if a local database is referenced by the numeral “<b>323</b>,” it should be understood that the reference may include any one, or all, of the local databases in the system <b>300</b>.

p-0029In an embodiment of the present disclosure, the NMS <b>312</b> of the home location <b>310</b> controls configuration of the system <b>300</b>. To implement mobility management within the system <b>300</b>, the NMS <b>312</b>, in one embodiment, pre-configures all radios operating on the system <b>300</b> as well as user group data in the central database <b>314</b>. The NMS <b>312</b> generates radio registration data comprised of a listing of radios that are registered with the system <b>300</b> and the user groups that are affiliated with each of the radios. Accordingly, a site <b>320</b> may only allow calls to be placed or received by a radio that is configured with the system <b>300</b>.

p-0030Radios that are configured to operate within the system <b>300</b> are registered with the system <b>300</b> in response to a registration event. A radio may be considered to be registered to the system <b>300</b>, or more particularly, to a site <b>320</b>. A registration event may occur automatically when a configured radio “enters coverage of a site” <b>320</b>, or when the registration event is initiated by the radio. A radio may be registered at a particular site <b>320</b> when the radio is turned on while within range of the site <b>320</b>, or when a radio previously out-of-coverage of the site <b>320</b> comes within range of the site <b>320</b> so that it is then within coverage. A registration event initiated by a radio may include data registration activities such as, for example, power-on/off of the radio and changing the radio channel or user group.

p-0031The radio registration data may be changed dynamically by the system <b>300</b> to add and/or remove radios from the system <b>300</b> and to change the user group affiliated with a radio. In the present disclosure, radios that are affiliated with a particular user group may be referred to as “belonging to,” being “affiliated with,” or being a “member of” that particular user group. It should be understood that not all radios may be affiliated with a user group; however, radios may be operable to scan, or listen to, one or more user groups.

p-0032In addition, the NMS <b>312</b> generates user group data, wherein the user group data may be comprised of a listing of normal user groups, critical user groups, a priority level for each normal and critical user group, and sites for which the normal and critical user groups are enabled. Accordingly, a site <b>320</b> may only allow calls to be placed to user groups that are configured with the system <b>300</b> and enabled in the site <b>320</b>.

p-0033The NMS <b>312</b> also generates critical user group data designating specific sites <b>320</b> in which a critical user group is enabled, and a period of time for which they are enabled. The user group data and critical user group data may be changed dynamically by the NMS <b>312</b>, in one embodiment. For example, the user group data and critical user group data may be changed to add/remove a user group, to select the designation of a user group to be critical or normal, to set/adjust the period of time for which a user group is designated as critical or normal, to set/adjust the priority level of a user group, to set/change the sites enabling a user group, or to set/adjust the period of time for which a critical user group is enabled in a particular site. In some embodiments, the radio registration data, user group data and critical user group data may be stored in at least one of the local database <b>323</b> of each site <b>320</b> in the system <b>300</b>, the central database <b>314</b>, or the data router <b>330</b>.

p-0034<figref idrefs="DRAWINGS">FIG. 4</figref> provides a more detailed illustration of an exemplary embodiment of a site <b>320</b> located within the system <b>300</b> shown in <figref idrefs="DRAWINGS">FIG. 3</figref>. The exemplary illustration <b>400</b> of <figref idrefs="DRAWINGS">FIG. 4</figref> shows a local site <b>320</b> having a VLR <b>324</b>, local database <b>323</b>, NIU <b>322</b>, repeater <b>325</b>, and radio tower <b>321</b>, wherein the NIU <b>322</b>, in one embodiment, further comprises a site controller application <b>415</b> and a channel controller application <b>420</b> (referred to hereinafter as “site controller” and “channel controller,” respectively). The site controller <b>415</b> is responsible for validation-checking of radios and user groups at the local site <b>320</b>, whereas the channel controller <b>420</b> is operable to control specific traffic channels to support communication with the repeater <b>325</b> to transmit and receive audio and data on a selected traffic channel. In <figref idrefs="DRAWINGS">FIG. 4</figref>, the VLR <b>324</b> and local database <b>323</b> are shown separate from the NIU <b>322</b> to maintain consistency with the system <b>300</b> shown in <figref idrefs="DRAWINGS">FIG. 3</figref> even though, as previously mentioned, in some embodiments they may reside within the NIU <b>322</b>.

p-0035Calls placed in the system <b>300</b> are typically handled within the site <b>320</b> in which the call originates, or is placed. As explained below, mobility management allows the system <b>300</b> to track the location and user group data of radios located within the system <b>300</b>. The location and user group data is used by the system <b>300</b> to place calls between the radios and user groups. Typically there are two types of calls that may be placed, an individual call or a group call (otherwise referred to as “user group call”). An individual call originates from one radio and connects to one other radio, whereas a group call originates from one radio and connects to one or more radios that are members of the user group for which the call is placed. As used throughout the present disclosure, the term “interested radios” refers to radios that are members of a user group for which a specific call is placed.

p-0036Individual calls occurring between a source radio (i.e., the radio placing the call) and a destination radio (i.e., the radio receiving the call) may be classified as a local call or inter-site call, depending upon the location of the destination radio relative to the site <b>320</b> within which the call is originated. When the source radio places an individual call at a local site <b>320</b>, the local channel controller <b>420</b> will request a radio validation from the local site controller <b>415</b>. The local site controller <b>415</b> will then look up both the source and destination radios in the local database <b>323</b> (or central database <b>314</b>) to verify that the radios are registered with the system <b>300</b>. Verification is then sent to the local channel controller <b>420</b>. If the call is valid (i.e., the source radio and destination radio are both registered with the system <b>300</b>), the local channel controller <b>420</b> will request a call connect from the local site controller <b>415</b>. If the source radio is not registered with the local site <b>320</b> but is configured with the system <b>300</b>, the source radio's initiation of the call acts as a registration event, whereby the source radio is registered with the local site <b>320</b>.

p-0037Because all databases <b>323</b> in the system <b>300</b> are assumed to be updated with the location and user group data for each radio in the system <b>300</b>, in one embodiment, the local site controller <b>415</b> may check the local database <b>323</b> to determine the destination radio's location. If the destination radio is located in the local site <b>320</b>, then the call is classified as a local call, meaning the call will remain within the local site <b>320</b>. However, if the destination radio is located in a remote site (not shown), then the call is classified as an inter-site call, meaning the call will be placed between the local site <b>320</b> and the remote site. If the call is an inter-site call, the local site controller <b>415</b> may contact the remote site controller (not shown) to set up the call. The local channel controller <b>420</b> then routes the call between the local site <b>320</b> and the remote site. In an embodiment of the present disclosure, the radios may be configured to allow or disallow individual calls.

p-0038By providing radio location and user group data through mobility management, the system <b>300</b> tracks not only the location of any radio registered with the system <b>300</b>, but also which user groups are available to receive a call at each site <b>320</b>. In an embodiment of the present disclosure, the system <b>300</b> dynamically routes group calls and allocates traffic channels based on the location of radios belonging to particular user groups within the system <b>300</b>. This dynamic call routing and traffic channel allocation may be referred to herein as “user group zoning.” For example, in accordance with <figref idrefs="DRAWINGS">FIG. 3</figref>, if a radio located at a site <b>320</b> (e.g. site <b>320</b>A) places a call for a “Police” user group, the system <b>300</b> will check to see if other sites in the system <b>300</b> (e.g. sites <b>320</b>B and <b>320</b>C) contain radios that are members of the “Police” user group. As previously mentioned, the term “interested radio” refers to a radio belonging to a user group of a call that has been placed. Sites <b>320</b> containing interested radios (i.e., radios that are members of the “Police” user group) allocate traffic channels for the call; otherwise the site <b>320</b> ignores the call by not allocating traffic channels for the call. User group zoning allows each site <b>320</b> in the system <b>300</b> to reserve RF resources by only allocating traffic channels for a user group call if there are interested radios on the site <b>320</b>. The details of user group zoning and group calls are described below.

p-0039When a group call is placed at a local site <b>320</b> in the system <b>300</b>, the local channel controller <b>420</b> may request a radio and user group validation from the local site controller <b>415</b>. The local site controller <b>415</b> will then look up both the source radio and the user group in the local database <b>323</b> (or central database <b>314</b>) to verify that the source radio is registered with the system <b>300</b> and the user group is registered with the system <b>300</b> and enabled at the local site <b>320</b>. Verification is then sent to the local channel controller <b>420</b>. If the call is valid (i.e., the source radio is registered with the system <b>300</b> and the user group is valid in the system <b>300</b> and enabled in the local site <b>320</b>), the local channel controller <b>420</b> will request a call connect from the local site controller <b>415</b>.

p-0040Since the local database <b>323</b> contains a listing of all radios, their location within the system <b>300</b>, and their user group affiliation, and the user group data located in the local database <b>323</b> contains a listing of all sites in the system <b>300</b> that enable the user group of the call being placed and whether the user group is designated as normal or critical for each site <b>320</b> enabling the user group, the local site controller <b>415</b> may determine if the call will remain local, or if it will need to connect an inter-site call with other sites <b>320</b> in the system <b>300</b>. If an inter-site call is necessary, the local site controller <b>415</b> may contact the remote site controller in each site participating in the call to set up the call. The local channel controller <b>420</b> then routes the call between the local site <b>320</b> and each site <b>320</b> participating in the call. The process for determining if a site may participate in a call is explained in greater detail below.

p-0041A site <b>320</b> may be determined to participate in the call based on the following criteria. If the site <b>320</b> is affiliated with the user group of the call, and the user group is designated as a normal user group for the site <b>320</b>, then the site <b>320</b> may allocate traffic channels to participate in the call if the site <b>320</b> has an interested radio. However, when a user group is designated as critical for the site <b>320</b>, the site <b>320</b> will always, in one embodiment, allocate resources for a call originating anywhere in the system <b>300</b> when the call is placed for the critical user group, even if the site <b>320</b> has no interested radios when the call is placed. The use of critical user groups allows for a radio belonging to a critical user group to move from one site <b>320</b> directly to another site <b>320</b> recognizing the user group as critical without dropping a call, even if there were no interested radios at the new site <b>320</b> when the call was placed. The possible additional bandwidth is reserved because of the “critical” nature and importance of the call and the need for added reliability.

p-0042A call that is already in process may be received at a new site <b>320</b> not currently allocating resources for the call if an interested radio moves to the new site <b>320</b> (regardless of whether the interested radio is participating in the call already in process), or a radio already on the new site <b>320</b> provides a mobility update to the system <b>300</b>, wherein the mobility update includes the user group for the call currently in process. When this occurs, the site <b>320</b> may allocate resources (if available) for the call, thereby allowing the radio to continue the call uninterrupted. Accordingly, a call requiring resources to be allocated dynamically at a new site <b>320</b> as just described is assumed to be a normal group call since a critical group call would already have resources allocated at the new site <b>320</b>.

p-0043To support mobility management, data is transmitted to and from each radio registered with the system <b>300</b> when the current traffic channel of a given radio is idle. This data may include a mobility update, a status message, or any other data communicated between the radio and components within the system <b>300</b>. In one embodiment of the present disclosure, the system <b>300</b> sends periodic data packets to each radio within the system <b>300</b> at a configured period of time (e.g., every two minutes), wherein the periodic data packets may be sent regularly at the configured time, or only when no voice or data traffic has been detected on a radio's traffic channel for the configured period of time. Receipt of any data or voice communication by the radio confirms to the radio that it is within coverage of the system <b>300</b>. However, if the radio fails to receive any data or voice communication within a given period of time (e.g., 5 minutes), the radio assumes that it is no longer within coverage of the system <b>300</b>. Accordingly, the radio may be programmed to provide an “out-of-coverage” indication to alert the radio operator that the radio is no longer within coverage of the system <b>300</b>. The out-of-coverage indication may include any combination of an audible, visual, and/or vibration indication. The out-of-coverage indication may continue until data or voice communication is received by the radio.

p-0044Radios operating within the system <b>300</b> may also be configured to support channel and/or user group scanning (otherwise referred to herein as “radio scanning”). Radio scanning allows radios to listen for activity of a number of pre-configured channels and/or user groups while the radio's current traffic channel is idle. It should be noted that during radio scanning, the radio's current traffic channel and user group are not changed; therefore, if communication is initiated by the radio during the radio scan, and the communication is not in response to channel activity on one of the scanned channels/user groups, the radio will use its currently-selected traffic channel and user group. However, if during the scan, communication is initiated by the radio in response to activity on one of the scanned channels/user groups, the radio, in one embodiment, will temporarily switch its transmitter to the scanned channel/user group so the communication will be transmitted to/from the channel/user group on which the activity was detected. After a period of inactivity on the channel/user group on which the activity was detected, the radio will revert back to its original traffic channel and user group and will continue scanning.

p-0045Because radios may scan multiple user groups, a single radio may be considered an interested radio for more than one user group or group call (when the radio is scanning). Therefore, if a radio is already participating in a group call, the radio may choose to ignore a new group call detected on its scanning channels/user groups if the new group call is of a lower priority than the group call in which the radio is already participating.

p-0046The system <b>300</b>, in certain embodiments, may be able to perform several functions over the air with respect to activity of a specific radio. For example, the system <b>300</b> may be able to verify over the air whether or not a radio is operational (i.e., on, functional, and within coverage) by sending a “radio check” command, and the system <b>300</b> may be able to disable or enable communication of a specific radio by sending a “radio inhibit/uninhibit” command. When a radio check command is requested, the NMS <b>312</b> may send the command to various VLRs <b>324</b> in the system <b>300</b>. The VLRs will forward the command to each local site <b>320</b> for transmission over the air to the radio. The radio will respond with a “Radio Check Acknowledged” signal sent to the radio's local VLR <b>324</b>, which forwards the response to the HLR <b>316</b>. The HLR <b>316</b> updates the central database <b>314</b> with the response. Receipt of the radio check acknowledged signal confirms to the system <b>300</b> that the radio is, indeed, operational.

p-0047The system <b>300</b> is able to disable an enabled radio by requesting a radio inhibit command. When a radio inhibit command is requested, the NMS <b>312</b> sends a radio inhibit control message to various VLRs <b>324</b> in the system <b>300</b>. Each VLR <b>324</b> forwards the radio inhibit control message to its respective local site <b>320</b>. Each site <b>320</b> then transmits the radio inhibit control message until a “radio inhibit complete” control message is received by the site's local VLR <b>324</b>. The radio inhibit control message is transmitted by the site <b>320</b> to the radio addressed by the control message. Once received, the radio sends a “radio inhibit acknowledged” message to its local site <b>320</b>, which sends a radio inhibit complete message to the local VLR <b>324</b>. The VLR <b>324</b> forwards the radio inhibit complete message to the HLR <b>316</b>, which propagates the message to various VLRs <b>324</b> in the system <b>300</b>. When a VLR <b>324</b> receives a radio inhibit complete message, it will send a request to its local site <b>320</b> to stop transmitting the radio inhibit control message.

p-0048The system <b>300</b> is also able to enable a disabled radio by sending a radio uninhibit control message to the disabled radio. When a radio uninhibit command is requested, the NMS <b>312</b> sends a radio uninhibit control message to each VLR <b>324</b> in the system <b>300</b>. Each VLR <b>324</b> forwards the radio uninhibit control message to its respective local site <b>320</b>. Each site <b>320</b> then transmits the radio uninhibit control message until a “radio uninhibit complete” control message is received by the site's local VLR <b>324</b>. The radio uninhibit control message is transmitted by the site <b>320</b> to the disabled radio addressed by the control message. Once received, the radio is enabled and sends a “radio uninhibit acknowledged” message to its local site <b>320</b>, which sends a radio uninhibit complete message to the local VLR <b>324</b>. The VLR <b>324</b> forwards the radio uninhibit complete message to the HLR <b>316</b>, which propagates the message to all VLRs <b>324</b> in the system <b>300</b>. When a VLR <b>324</b> receives a radio uninhibit complete message, it will send a request to its local site <b>320</b> to stop transmitting the radio uninhibit control message.

p-0049Mobility management, in one embodiment, allows the system <b>300</b> to track the location of a radio, when the radio accesses the system <b>300</b> from any site <b>320</b>, by receiving from the radio, in one embodiment, time-stamped location and/or user group data packets known as “mobility updates.” Transmission of the mobility updates may occur once the radio detects that the current traffic channel is idle. The term “mobility update” may be used throughout the present disclosure to refer to the time-stamped data packets containing radio location and/or user group data, whereas the term “mobility update event” may be used to refer to the act of sending and/or receiving a new mobility update between components of the system <b>300</b>. Additionally, the term “local mobility update event” refers to a mobility update event originating within a local site <b>320</b>, whereas the term “remote mobility update event” refers to a mobility update event originating outside the local site <b>320</b>. In local mobility update events, mobility updates may be pushed to the HLR <b>316</b> from the VLR <b>324</b> of the local site <b>320</b> for distribution to the rest of the system <b>300</b>, whereas in remote mobility update events, mobility updates may be pushed down to the VLR <b>324</b> of the local site <b>320</b> by the HLR <b>316</b>. For simplicity, mobility updates are described herein as having “location and user group data;” however, it should be appreciated that although mobility updates typically include both location and user group data, in some embodiments, the mobility update may not include one of the location data or the user group data.

p-0050The location and user group data provided in a mobility update may be stored in multiple components of the system <b>300</b>. For example, the location and user group data may be stored in the central database <b>314</b>, local databases <b>323</b>, and/or data router <b>330</b>. In some embodiments, the location and user group data may even be stored in an internal memory or register located in the HLR <b>316</b> and VLRs <b>324</b>. In accordance with the present disclosure, when reference is made to knowledge of a radio's location and user group data by the system <b>300</b>, it should be understood that the data may be stored in multiple locations within the system <b>300</b> as described above.

p-0051In an embodiment of the present disclosure, local mobility update events will trigger the local VLR <b>324</b> to push the mobility updates to the HLR <b>316</b>, in one embodiment, when the mobility update indicates a change in the location, such as movement from one site <b>320</b> to another site <b>320</b>, or a change in the user group data of the radio initiating the mobility update. Remote mobility updates received at the HLR <b>316</b>, from other VLRs in the system, will trigger the HLR <b>316</b> to push the mobility updates down to the VLR <b>324</b>, which will update the local database <b>323</b>. Mobility update events are described in greater detail below.

p-0052Mobility update events may be initiated in response to a registration event occurring at a site <b>320</b>, or in response to radio activities such as, for example, initiating a “Request-to-Talk”(RTT), emergency alarm transmission, status message transmission, and “Push-to-Talk” (PTT). These radio activities are referred to as implicit registration events because operation of the event may indicate that the radio is registered with the site <b>320</b>; however, if the radio is not registered, the implicit registration event will trigger the registration of the radio with the site <b>320</b> if the radio is configured with the system <b>300</b>.

p-0053In general, a mobility update event may be initiated by a radio when there is a change in the radio's location or user group data, or if the radio incurs a power-on/off, change of channel, RTT, emergency alarm transmission, status message transmission, PTT, or other events that result in a change to the operation or status of the radio. Additionally, it should be appreciated that a mobility update event may be initiated in response to events other than those provided herein; and therefore, may be initiated not only by the radio itself, but also by components within the system <b>300</b>. For example, a dispatch console <b>340</b> may command a site <b>320</b> to request mobility updates from all radios located at the site <b>320</b>.

p-0054As described above, local mobility update events take place within a local site <b>320</b> upon occurrence of any one of several events (i.e., radio enters coverage of the site <b>320</b>, radio powers on or off, radio channel is changed, etc). When a local mobility update event occurs in one implementation, an initial check is performed at the local site <b>320</b> to determine whether the mobility update contains a change in the location or user group data already known for the radio initiating the local mobility update event. <figref idrefs="DRAWINGS">FIG. 5</figref> illustrates the steps and components involved in an exemplary initial check of a local mobility update event.

p-0055In step <b>501</b>, a radio <b>520</b> initiates a local mobility update event by transmitting a mobility update across a traffic channel when the traffic channel is idle. The mobility update is received by the radio tower <b>321</b> and transmitted to the repeater <b>325</b> in step <b>502</b>. In step <b>503</b>, the repeater <b>325</b> transmits the mobility update to the channel controller <b>420</b>. The channel controller <b>420</b> transmits the mobility update to the data router <b>330</b> and VLR <b>324</b> in steps <b>504</b> and <b>505</b>, respectively. Although steps <b>504</b> and <b>505</b> are shown separately in <figref idrefs="DRAWINGS">FIG. 5</figref>, it should be understood that these steps may occur simultaneously as a single event. In step <b>506</b>, the VLR <b>324</b> updates the local database <b>323</b> with the radio <b>520</b> user group data (e.g. user group affiliation) and location data (i.e., site affiliation data) contained in the mobility update. In the present embodiment, the location and user group data of the radio <b>520</b> is stored in both the data router <b>330</b> and the local database <b>323</b>. If the pre-existing data in the local database <b>323</b> matches the data contained in the mobility update, then the initial check process ends here since there has been no change to the radio's location or user group data. However, if the mobility update contains different radio location or user group data, then the local site <b>320</b> will push the mobility update up to the rest of the system <b>300</b> as explained below and illustrated in <figref idrefs="DRAWINGS">FIG. 6</figref>.

p-0056<figref idrefs="DRAWINGS">FIG. 6</figref> is an updated version of <figref idrefs="DRAWINGS">FIG. 5</figref> illustrating the steps and components of <figref idrefs="DRAWINGS">FIG. 5</figref> as well as the steps and components involved in an exemplary mobility update event after it has been determined that the mobility update contains new location or user group data, and therefore is to be pushed to the rest of the system <b>300</b>. After updating the local database <b>323</b> with the new location and/or user group data as described above, the VLR <b>324</b> sends a command to the site controller <b>415</b> to send the location data contained in the mobility update to the data router <b>330</b> in steps <b>507</b> and <b>508</b>. The VLR <b>324</b> then pushes the mobility update to the HLR <b>316</b> in step <b>509</b>. Upon receipt of the mobility update, the HLR <b>316</b> updates the central database <b>314</b> with the mobility update in step <b>510</b>. In step <b>511</b>, the HLR <b>316</b> pushes the mobility update to other VLRs in the system <b>300</b>. Although it is not illustrated in <figref idrefs="DRAWINGS">FIG. 6</figref>, upon receipt of the mobility update, the other VLRs in the system <b>300</b> update their respective local databases with the mobility update. It should be noted that, with respect to the VLRs in the other sites, this mobility update event would be considered a remote mobility update event since it originated from another site. Updating all respective local databases <b>323</b> in response to the mobility update ensures that databases <b>323</b> within the system <b>300</b>, the central database <b>314</b>, and the data router <b>330</b> are updated with the mobility update from the radio <b>520</b> initiating the mobility update event.

p-0057Although it is not illustrated in <figref idrefs="DRAWINGS">FIGS. 3-6</figref>, in some embodiments, upon receiving a mobility update, the HLR <b>316</b> may push the mobility update to all VLRs <b>323</b> in the system <b>300</b>, including the local VLR <b>323</b> originally providing the mobility update to the HLR <b>316</b>. In this embodiment, the local VLR <b>323</b> may not send a command to its local site controller <b>415</b> to send the location data to the data router <b>330</b> until after it receives the mobility update from the HLR <b>316</b>.

p-0058In an example in accordance with the embodiments illustrated in <figref idrefs="DRAWINGS">FIGS. 3-6</figref>, if a radio <b>520</b> is powered on within range (coverage) of site <b>320</b>A, the radio <b>520</b> initiates a mobility update event—in this case, the mobility update could be initiated by a registration event resulting from the power-on of the radio <b>520</b>. It should be noted that this registration event prompts the site controller <b>415</b> to validate the radio <b>520</b> and its user group. The radio <b>520</b> monitors its current traffic channel for activity and transmits the mobility update through the radio tower <b>321</b> to the router <b>325</b> when the traffic channel is idle. The router <b>325</b> then sends the mobility update to the channel controller <b>420</b>, which sends the mobility update to the VLR <b>324</b> and data router <b>330</b>. The VLR <b>324</b> then stores the mobility update in the local database <b>323</b>A. With respect to site <b>320</b>A, the initiation of the mobility update is considered a local mobility update event.

p-0059If the mobility update provides new location or user group data, the VLR <b>324</b>A sends a command to the site controller <b>415</b>A to send a data registration packet to the data router <b>330</b>. The VLR <b>324</b>A then pushes the mobility update to the HLR <b>316</b> where it is stored in the central database <b>314</b>. The HLR <b>316</b> then pushes the mobility updates to VLRs <b>324</b>B and <b>324</b>C. Upon receipt of the mobility update, the VLRs <b>324</b>B and <b>324</b>C then store the mobility update in local databases <b>323</b>B and <b>323</b>C, respectively. With respect to sites <b>320</b>B and <b>320</b>C, receipt and storage of the mobility update is considered a remote mobility update event since the mobility update originated from site <b>320</b>A. Accordingly, local databases <b>323</b>A, <b>323</b>B and <b>323</b>C, and central database <b>314</b> contain the mobility updates and, thus, are up-to-date.

p-0060In one implementation, a site <b>320</b> may send periodic information packets to the NMS <b>312</b>, to which the NMS <b>312</b> replies with an acknowledgement confirmed or failed signal thereby indicating whether or not a proper connection exists between the site <b>320</b> and the home location <b>310</b>. Consequently, both the site <b>320</b> and the NMS <b>312</b>, and thus, the home location <b>310</b>, may detect loss of a connection. Additionally, when a VLR <b>324</b> and the HLR <b>316</b> communicate, each provides confirmation, or acknowledgement, that communication was received. Thus, a site <b>320</b> may determine that the HLR <b>316</b> is nonresponsive, or down, when the VLR <b>324</b> fails to receive confirmation from the HLR <b>316</b>; and the HLR <b>316</b> may determine that the VLR <b>324</b> is nonresponsive when the HLR <b>316</b> fails to receive confirmation from the VLR <b>324</b>. Accordingly, two communication error conditions may exist: 1) the HLR <b>316</b> is down, and thus, is disconnected from (and unable to communicate with) all VLRs <b>324</b> in the system <b>300</b>; and 2) a VLR <b>324</b> is down, and thus, is unable to communicate with the HLR <b>316</b> and other VLRs <b>324</b>. If a connection between a site <b>320</b> and the home location <b>310</b> is lost, each disconnected site <b>320</b> may operate using its respective local database <b>323</b> in a stand-alone mode as described below.

p-0061In the first condition, wherein the HLR <b>316</b> is down and is unable to communicate with all VLRs <b>324</b> in the system <b>300</b>, a VLR <b>324</b> may send mobility updates directly to other VLRs <b>324</b> within the system <b>300</b> for storage in their respective local databases <b>323</b> by sending a multicast mobility update. For example, in accordance with <figref idrefs="DRAWINGS">FIG. 3</figref>, if a local mobility update event occurs at site <b>320</b>A, and the VLR <b>324</b>A is unable to communicate with the HLR <b>316</b>, the VLR <b>324</b>A may transmit the mobility update directly to VLRs <b>324</b>B and <b>324</b>C for storage in local databases <b>323</b>B and <b>323</b>C.

p-0062Once the HLR <b>316</b> is reconnected with the VLRs <b>324</b>, a synchronization process between each reconnected VLR <b>324</b> and the HLR <b>316</b> may occur, wherein the central database <b>314</b> is updated with the mobility updates stored in the local databases <b>323</b> of the reconnected VLRs <b>324</b>. Because the mobility updates are time-stamped, the system <b>300</b> may confirm that the most recent mobility updates are stored in all databases (local databases <b>323</b> and central database <b>314</b>) within the system <b>300</b>.

p-0063In accordance with the second condition, wherein a VLR <b>324</b> is down and is disconnected from the HLR <b>316</b> and other VLRs <b>324</b>, if the HLR <b>316</b> is aware of the existence of the disconnected VLR <b>324</b>, mobility updates, which may include radio data such as radio location data or radio user group data, received from other connected VLRs <b>324</b> may be queued in the HLR <b>316</b> until communication is reestablished with the disconnected VLR <b>324</b>. Once communication is reestablished, the mobility updates are pushed to the reconnected VLR <b>324</b>. If the HLR <b>316</b> is unaware of the disconnected VLR <b>324</b>, upon connection, the local database <b>323</b> of the previously disconnected VLR <b>324</b> will be synchronized with the mobility updates of the central database <b>314</b>.

p-0064It should be appreciated by those of ordinary skill in the art, that certain components of the system <b>300</b> may be integrated with others without departing from the scope of the application as set forth in the claims below. For example, the home location <b>310</b> may not include a separate central database <b>314</b>. As such, information that is disclosed as being stored in the central database <b>314</b>, may alternatively be stored in an onboard memory or register located in the HLR <b>316</b>. Additionally, certain components, modules and functions may be integrated into one unit or separate. For example, in some embodiments, the data router <b>330</b> may be combined with the HLR <b>314</b>.

p-0065<figref idrefs="DRAWINGS">FIG. 7</figref> is provided as a general description of one example embodiment for providing mobility management and out-of-coverage indication in a conventional land mobile radio system. The operations provided in this embodiment may be performed by various components within the LMR system. A flowchart <b>700</b> is shown in <figref idrefs="DRAWINGS">FIG. 7</figref>, wherein one iteration of the method starts at <b>702</b> and a traffic channel is monitored at <b>704</b>. At <b>706</b>, data packets are transmitted across the traffic channel from an LMR site to a radio. If the radio receives the data packets at <b>708</b>, then at <b>710</b> the radio determines if the traffic channel is idle. However, if the radio does not receive the data packets at <b>708</b>, then at <b>712</b> the radio determines if it has detected activity on the traffic channel during an allotted period of time. It should be appreciated that determining if the radio has detected activity on the traffic channel during an allotted amount time may be performed at any time and regardless of whether or not the radio receives the data packets; however, in the event that the radio does receive the data packets, the determination at <b>712</b> may be unnecessary in certain implementations. If the radio has detected activity (e.g., receipt of voice or data communication) on the traffic channel within the allotted amount of time, then the iteration ends or restarts and the radio continues to monitor the traffic channel; otherwise, the radio indicates that it is out-of-coverage at <b>714</b>.

p-0066If the radio received the data packets at <b>708</b>, the radio waits until the traffic channel is idle before sending current radio location and user group data across the traffic channel to the LMR site at <b>716</b>. As previously stated, in some embodiments, the location data may be the site to which the radio is communicating, or coordinate data such as that provided by a Global Positioning System (GPS). If either the radio location data or the radio user group data, for example, sent to the LMR site is determined to be new (i.e., different than what was previously stored for the radio in the LMR system) at <b>718</b>, then the LMR system is updated with the new location and/or user group data at <b>720</b>; otherwise, the iteration ends (or starts over) at <b>722</b>.